1. Field of the Invention
A personal mobility vehicle or powered wheelchair comprising a seat movably mounted to a carriage to control the position of the seat relative to the carriage during operation of the personal mobility vehicle.
2. Description of the Prior Art
Personal mobility vehicles commonly known as wheelchairs have been used to improve the mobility of disabled or handicapped persons. In instances where an individual has limited or no use of his or her legs, a wheelchair may be the sole means of transportation.
It is desirable for a paralyzed person to be able to shift or move his or her body on the wheelchair from time to time. This periodic shifting of the weight of a person's body is essential to prevent ulcers, infection and possible gangrene. Various wheelchairs have been designed to permit the seat to be tilted to shift the body weight to permit circulation in the essential skin areas.
U.S. Pat. No. 5,356,172 shows a hand-propelled wheelchair frame element to which is mounted a pair of large drive wheels and a pair of front caster wheels. A seat unit is slidably mounted on the frame in such a manner as to be manually slidable in a plurality of positions along the frame element to vary the weight distribution of the user and the seat unit with reference to the axis of the drive wheels.
U.S. Pat. No. 5,297,021 discloses a wheelchair seat backrest assembly with a counter-balance to provide equilibrium. A control loop is included on the sliding backrest to sense the onset of shear and compensate the backrest to a zero shear position during recline.
U.S. Pat. No. 4,274,503 relates to a wheelchair assembly including an occupant seat having a central shaft for mounting the seat on an undercarriage for universal tilting movement and vertical movement along the shaft axis and for rotation about such axis.
U.S. Pat. No. 4,759,561 teaches a wheelchair comprising an underframe with front and rear wheels and a seat which can be tilted forward and backward relative to the underframe in such a way that the overall weight distribution of seat part and wheelchair user essentially assumes a fixed position relative to the underframe.
U.S. Pat. No. 5,121,806 discloses a power wheelchair including a torsional frame and stability frame to provide automatic compensation for directional tracking errors caused by shifts in the mass center of an occupant.
GB 2 141 980 shows a wheelchair comprising a chassis which is longitudinally adjustable. The relative position of the seat and the rear wheels may be adjusted to vary the weight distribution of the wheelchair. As a result the stability against tipping may be increased when obstructions and obstacles such as curbs are negotiated.
GB 2 048 791 discloses a wheelchair comprising a frame with four wheels and a seat mounted on the frame for forward and rearward adjustment by means of slides. The seat is mounted on a pivotal parallelogram linkage. The seat comprises a tiltable backrest portion and raisable arms.
U.S. Pat. No. 3,891,269 teaches a mounting mechanism for a seat reciprocally movable on a surface is provided with a seat support having wheels for rolling engagement on the surface. A locking member is selectively movable between a locking position in which the locking member is releasably engaged between at least one of the wheels and the surface to prevent movement of the seat support on the surface in one direction and a released position in which the locking member is not engaged with both the one wheel and the surface to permit movement of the seat support along the surface in the one direction.
U.S. Pat. No. 3,952,822 shows an electrically powered wheel-chair. To improve stability, the weight distribution of the batteries is located on the same side of the longitudinal axis of the chair as the steering wheel.
Additional examples of the prior art are found in U.S. Pat. Nos. 4,951,766; 5,301,964 and GB 2 244 684.